In a typical die casting application, a charge of molten metal is delivered from a shot barrel through a gooseneck passage and through a nozzle to the mold cavity where the die cast parts are formed. It is critical to maintain the metal in a liquid state as it flows from the shot barrel to the mold cavity and it is particular critical to maintain the metal in a molten state as it moves through the gooseneck passage and the die casting nozzle. The metal is typically maintained in a molten state as it moves from the shot barrel to the mold cavity by the use of one or more torches which are directed against the gooseneck passage and against the nozzle to ensure that the flowing metal is maintained at a temperature above its melting temperature. These torches typically burn a mixture of a combustible gas, such as methane, and air. Rarely is this mixture controlled to burn at a ratio less than 10 to 1. When CH.sub.4, is burned at an air to gas pressure ratio less than 10 to 1 the temperature of the flame is lowered proportionately. It is common place to use the high range of the flame temperature. Specifically in an attempt to speed up production or otherwise optimize the die casting operation, the operator commonly increases the air pressure to an extent such that the flame temperature becomes so great as to cause localized erosion of the metal along the central bore of the nozzle and/or so as to heat the molten metal to a temperature well above the temperature required to maintain it in a molten state with the result that the cooling time for the cast article becomes excessive.
Various attempts have been made in the past to limit the ability of the operator to increase the air pressure to an undesirably high level but such prior art attempts have either been ineffective in preventing the operator from increasing the air pressure or have been so expensive or complicated as to be impractical.